This invention relates to an apparatus for measuring a thickness of a hard layer formed by hardening and a thickness of a buildup of a material different from a base material in a non-destructive manner using transverse waves of ultrasonic waves.
Generally, members which tend to be strongly abraded when gears, rolls or the like are used have their surfaces hardened in order to reduce abrasion as much as possible, thereby forming hard layers on their surfaces. An accurate grasp of a thickness of the hard layer is a very critical matter to be checked in view of guarantee of the quality of the abrasive members and their estimated lives.
A conventional method for measuring the thickness of the hard layer is, for example, such that the hard layer is cut in its depth direction and the cut surface is macroscopically observed after being abraded and etched, and that the thickness of the hard layer is grasped by measuring hardness at several points on the cut surface. However, this method requires much labor in order to measure the hardness and necessitates a destructive examination, thus a random examination. Measurement costs are also tremendously expensive.
As a countermeasure, a method using ultrasonic waves has been used to measure the thickness of the hard layer. This method employs water immersion or local water immersion to improve a measurement accuracy. An example of the use of water immersion to measure the thickness of the hard layer is disclosed in Japanese Unexamined Patent Publication No. 3-130658.
A variety of flaw detection probes used in association with the local water immersion have been proposed. These probes include a probe holder for setting a probe at a desired distance in water from a material to be measured (disclosed in Japanese Unexamined Utility Model Publication No. 3-81553), a flaw detection probe which has a water bag before a sensing surface and a friction resistant contact film on a contact surface of the water bag with a material to be measured to prevent a water leak (disclosed in Japanese Unexamined Utility Model Publication No. 2-67259), and a probe shoe capable of adjusting a distance in water by moving a probe and a material to be measured and adjusting the sensitivity, and of detecting a flaw on a curved surface such as of a pipe (disclosed in Japanese Unexamined Utility Model Publication No. 57-116863).
The flaw detection probe disclosed in the Japanese Unexamined utility Model Publication No. 2-67259 transmits ultrasonic waves in such a manner that their transverse waves are obliquely incident upon the material to be measured. It has been known that the use of the transverse waves of the ultrasonic waves is effective in detecting a defect in a welded portion of a plate and detecting the depth of a crack on the surface.
However, the transverse waves of the ultrasonic waves employed in a variety of conventional apparatuses are limitedly used to detect a flaw such as an internal defect or a crack. These apparatuses do not actively use the transverse reflected waves caused by an irregular reflection (diffusion) produced in a grain boundary in order to obtain the measurement result, but rather eliminate the reflected wave as noises.